1. Field
The present disclosure relates to a power transmission apparatus for driving a plurality of driven gears by a single drive gear. More particularly, the present disclosure relates to an arrangement of a drive gear and a plurality of driven gears engaged with the drive gear that can reduce vibration of a power transmission apparatus.
2. Description of the Related Art
For cost reduction, a power transmission apparatus used in an image forming apparatus may be configured for one driving source to drive a plurality of driven members. In such a case, a drive gear disposed at the one driving source is formed to rotate a plurality of driven gears connected to the plurality of driven members.
FIG. 1 illustrates a case in which a single drive gear 1 is engaged with two driven gears 5 and 6. The drive gear 1 is fixed to a shaft 3 of a motor that is a driving source, and the top and bottom of the drive gear 1 are meshed with first and second driven gears 5 and 6. The first and second driven gears 5 and 6 are connected to first and second driven members (not illustrated), respectively. Accordingly, when the drive gear 1 rotates, the first and second driven gears 5 and 6 are rotated to transmit power to the first and second driven members.
For example, as illustrated in FIG. 1, if the number of teeth of the drive gear 1 is ten (10), the number of the driven gears 5 and 6 meshed with the drive gear 1 is two (2), and an installation angle between the two driven gears 5 and 6 is approximately 180 degrees, P is an integer.
Here, P is defined as Z/N (namely, P=Z/N).
Z is the number of teeth of the drive gear 1. In the case of FIG. 1, Z is ten (10). N is the number of the plurality of driven gears 5 and 6. In the case of FIG. 1, N is two (2). Accordingly, P=10/2=5 so that P is an integer.
As illustrated in FIG. 1, if the installation angle between the two driven gears 5 and 6 is approximately 180 degrees and P is an integer, when each of the first driven gear 5 and the second driven gear 6 are engaged with the drive gear 1, gear engagement is generated at the same phase so that the gear engagement phases are superimposed. Thus, if the gear engagement phases are superimposed, a lateral force is small, but transmission error increases so that a torsional force acts significantly in a rotation direction of the gear. Here, the transmission error refers to difference between a theoretical position of a gear and an actual position of the gear, and is generated by the design and manufacturing errors of the gears and transformation of the gears when the gears are engaged with each other. FIG. 2 is a graph showing that the transmission error is increased when the gear engagement phases are superimposed. From FIG. 2, it can be seen that the transmission error is increased when the gear engagement phases are overlapped.
The transmission error of the gear is a cause of an excitation force for generating vibration, and the excitation force induces the structural vibration of an entire apparatus in which the drive gear and a plurality of driven gears are installed. Accordingly, when the transmission error of gears in the power transmission apparatus of the image forming apparatus is large, jitter occurs, thereby adversely affecting images formed by the image forming apparatus.